It is known that mono-1-olefins (α-olefins), including ethylene, can be polymerized with catalyst compositions employing titanium, zirconium, vanadium, chromium, or other metals, often combined with a solid oxide and in the presence of cocatalysts. These catalyst compositions may be useful for both homopolymerization of ethylene, as well as copolymerization of ethylene with comonomers such as propylene, 1-butene, 1-hexene, or other higher α-olefins. Therefore, there exists a constant search to develop new olefin polymerization catalysts, catalyst activation processes, and methods of making and using catalysts, that will provide enhanced catalytic activities and polymeric materials tailored to specific end uses.
One type of transition metal-based catalyst system comprises metallocene compounds, which have shown promise in tailoring polymer properties. However, there remain significant challenges in developing catalysts that can provide custom-made polymers with a specific set of desired properties. Further, it is of interest to develop metallocene-based catalytic systems that can be activated with activating agents that do not require relatively expensive methylaluminoxane, yet still provide relatively high polymerization activities.
What are needed are new catalyst compositions and methods of making the catalyst compositions that afford high polymerization activities, and will allow polymer properties to be maintained within the desired specification ranges.